In work areas such as mines a danger of atmosphere contamination detrimental to workers' well-being is always present. A fire may deplete the air of oxygen and fill the work area with smoke particles which interrupt regular breathing processes. Oxygen may also be removed by the sudden and voluminous incursion of a foreign gas into the work area from newly opened fissures in the walls of the mine. Other dangers to personnel include the leaking of poisonous fumes into the air and a heavy loading of the atmosphere with dust particles, e.g. upon a cave-in.
Generally, oxygen-supplying devices for application upon the occurrence of such an incipiently disastrous event are too heavy and bulky to be continually worn or carried by personnel working at a mine site. Such devices are usually placed by the individual workmen on the ground at distances of ten to twenty meters from the site of the actual mining operations. The devices include eye glasses, nose clamps, mouthpieces connected to hoses extending from oxygen tanks, and valves for permitting oxygen flow from the tanks to the mouthpieces.
The disadvantages of using such oxygen-rescue devices is the relatively long time required to set the devices into operation. The manipulations of the nose clamps, the mouthpieces, the tanks and the valves may be complex and extensive. In addition, there is the time necessary to reach the devices from the mining site. Smoke and dust particles may inhibit vision, increasing the time it takes to locate the breathing apparatuses and thereby incrementing the probability of casualty. Uncertainty as to the location of the devices and as to the time available for application thereof induces panic which further aggravates the situation.
Another kind of breathing apparatus is known in which a blower or fan forces air from the atmosphere through a filter and into a space between a visor and the face of a user, the filtered air together with exhalations of the user leaving this space via an opening or gap between the bottom of the visor and the chin or the neck of the user. The outflow of air prevents the entry of poisonous or noxious fumes through the gap into the spacer at the user's face.
A disadvantage of such a breathing device is that it is ineffective in cases involving a depletion of atmosphere oxygen, e.g. owing to a fire or voluminous gaseous incursion. The fan and filter only remove noxious components from the air and are unable to supply oxygen in the event of a lack thereof.